Add vendor and base_model_url

Applies the provenance fields from ai-portal-model-schema#27, following the convention used across the Marvik catalogue. vendor is the upstream developer of the source baseline (Google), not the organisation that quantised it. metadata.yaml only.

metadata.yaml

@@ -4,6 +4,8 @@ task_type: text-generation
 title: Gemma-4-E2B 8da4w — ExecuTorch
 id: Arm/gemma-4-e2b-text-executorch
 base_model_id: google/gemma-4-E2B
+vendor: Google
+base_model_url: https://huggingface.co/google/gemma-4-E2B
 profile: Arm-Optimized
 weight_dtype: int4
 model_size_mb: 2563.959